1. Field of the Invention
The present invention relates to a bending tool mounted on a press bending machine (also called a press brake) for bending mechanical parts, such as a metal plate.
2. Description of the Related Art
Japanese Patent No. 1707773 discloses a bending tool proposed by the present applicant. The disclosed bending tool includes two dies, each of which includes a die body, a blade and a bending block. The blade is attached to an end of the die body. An edge of the blade has an angle of substantially 90 degrees that is bisected by a vertical blade parting line (i.e., a center line) The bending block is disposed adjacent to the blade with an adjustable space formed therebetween. The bending block and the blade altogether define a space along a direction substantially perpendicular to an edge surface of the blade. These dies oppose each other with the blade parting line of the first die being located at the center of the space between a blade parting line and a blade-side inner end edge of a bending block of the second die. A work (typically a metal plate) is placed on the lower die for a pressing operation. The blade edge of the upper die folds the work to the right angle at an area they are in contact with each other by pressing into the space formed adjacent to the blade of the lower die. The blade of the upper die is stopped when supported by an outside edge (which is a longer edge) of the blade edge and a chamfered face of the bending block. At the same time, the blade edge of the lower die folds the work to the right angle at an area they are in contact into the space formed adjacent to the blade of the upper die. The blade of the lower die is stopped when supported by an outside edge (which is a longer edge) of the blade edge and the chamfered face of the bending block. In this manner, a Z-shaped fitting is obtained.
In this bending tool, any one of the blade and the bending block is integrally formed with the die body and the other is provided separately. The separately provided one is fastened to the integrated one by a screw with a spacer disposed therebetween. The blade and the bending block are removably attached to the die body. Precise supporting surfaces of the blade and the bending block, which are press bending members, may be provided during production of the die body and thus a more precise bending tool may be provided. Since either the front side or the back side of the blade or the bending block is open when the die body operates, the bending tool is hardly interfered by projected portions on the die body, which may improve operational efficiency. If an edge of the removable blade or the bending block chips, the blade or the bending block may be removed and repaired, or may be replaced by an alternative part, which may be advantageous in maintenance. As described above, the related art bending tool has many advantageous effects.
The related art bending tool, however, has the following drawbacks.
(1) The blade of each die has the blade edge of substantially 90 degrees, which is bisected by the blade parting line. An angle formed by the blade parting line of each die and the edge outside with respect to the blade parting line equals to an angle formed by the blade parting line and the edge inside with respect to the blade parting line. The dies oppose each other with the blade parting line of the first die being located at the center of the space between the blade parting line and the blade-side inner end edge of the bending block of the second die. With this configuration, the work may be bent downward with respect to the horizontal direction from a folding point of the second, lower die to substantially 45 degrees. Thus, if the work is elongated (compared with a material to be processed of standard length), the work, especially the lower end thereof, may possibly collide with mechanical parts or the neighborhood thereof, which may hinder the bending operation. Most of the works to be processed with such a bending machine are elongated, however, and it is therefore needed to remove neighborhood obstacles to prevent collisions between (the lower end of) the work and (a part of) the bending machine. As a result, operational efficiency may be decreased.
(2) Since the bisected blade edge of each die folds the work to the right angle at an area they are in contact with each other by pressing into the space formed adjacent to the blade of the lower die, the work is bent in a rapid motion and may therefore be easily damaged. In addition, the work, especially the lower end thereof, is rapidly moved downward from the horizontal direction by 45 degrees, which may sometimes be unsafe to the operating personnel.
(3) Since the work is pressed with the blade edges of the dies misaligned with each other during a relative movement of the upper and the lower dies, it is likely that the dies are displaced from each other in the process of the pressing operation. Especially the lower die is more likely to be displaced since it is fastened to the table only with a screw. It is therefore difficult to elongate the metal mold or connect metal molds so as to extend the bending length.
In view of the aforementioned circumstances, an object of the invention is to provide a bending tool which may be used to reliably bend elongated (compared with materials to be processed of standard length) works without causing collisions with mechanical parts or the neighborhood thereof. Another object is to provide a bending tool in which the works are not likely to be damaged during the bending operation. A further object is to provide a bending tool which may be safe to the operating personnel. A still further object is to provide a bending tool in which misalignment of the dies may be reduced to improve machining precision. Yet another object is to provide a bending tool in which the metal mold may be elongated to increase the bending length.